Most of EMD's prime movers had quite a lot of stretch in them, it was mostly a trade - off between horsepower & durability. I recall reading of an EMD field service rep ( maybe Preston Cook ??? ) walking into Erie Lackawanna's Hornell shop, where he saw a recently rebuilt SD-45 20V645 on the test stand, easily putting out 4000+ H.P. !!! The 20V645 prime mover in Espee's SD-45X units produced 4200 H.P. by simply resetting the governor to 950 RPM. Also as noted above by Hot Water, the electronics and traction motors of the era were not quite the equal of the prime movers. The " Dash - 2 " 3-axle Flexicoil HT-C truck was also a big improvement, allowing the SD-40-2 to approach the SD-45 in tractive effort with only 16 cylinders / 3000 H.P. net.